This invention relates to a wheeled carriage for supporting a patient in a substantially horizontal position, and, more particularly, to a wheeled carriage having at least one auxiliary wheel selectively positionable with the floor surface. The auxiliary wheel can be raised or lowered by activation of control elements including a cam device. A power drive system enables driving of the auxiliary wheel to move the carriage.
Wheeled carriages for supporting a patient in a substantially horizontal position are well known in the art and a representative example of an early version of such a device is illustrated in Dr. Homer H. Stryker""s U.S. Pat. No. 3,304,116, reference to which is incorporated herein. Dr. Stryker""s innovative wheeled carriage included a fifth wheel which is raisable and lowerable by an attendant directly manually manipulating the wheel support frame oriented beneath the patient supporting portion of the wheeled carriage. The fifth wheel is positioned at substantially the center of the undercarriage such that usually the rear castered wheels and the fifth wheel support the carriage when the fifth wheel is deployed. However, the front castered wheels and the fifth wheel may also support a patient on the wheeled carriage depending on the position of the patient. Therefore, the wheeled carriage of U.S. Pat. No. 3,304,116 can teeter between the front and rear castered wheels when a patient is being moved thereon with the fifth wheel deployed.
In use, on an uneven floor surface, the fifth wheel disclosed in U.S. Pat. No. 3,304,116 can temporarily be in an extended position, but out of contact with the floor. For example, if a carriage begins movement up a ramp, the change in grade of the floor surface can cause the extended fifth wheel to lift from the floor. In the carriage of U.S. Pat. No. 3,304,116, the loss of contact with the floor can be a minor inconvenience. However, for a driven auxiliary wheel selectively positionable with the floor surface, loss of contact may lead to slipping or free rotation of the auxiliary wheel. Recontact between the auxiliary wheel and the floor may cause sudden acceleration of the carriage.
Accordingly, it is an object of this invention to provide a wheeled carriage for supporting a patient in a substantially horizontal position having an arrangement so that at least one driven auxiliary wheel, when in the extended position, maintains contact with the floor surface even if the floor surface is uneven or has a lower surface where the auxiliary wheel is positioned relative to the other wheels.
Controlling the speed and velocity of powered auxiliary wheels can be difficult because relatively slow stopping and starting is necessary to provide smooth acceleration and deceleration for wheeled carriages, especially carriages designed to transport persons with medical conditions.
It is a further object of this invention to provide a power drive control circuit for smooth acceleration and deceleration of the wheeled carriage by controlling driving of an auxiliary wheel.
The objects and purposes of the invention are met by providing a wheeled carriage for supporting a patient in a substantially horizontal position. The wheeled carriage includes a patient support having a length, opposing ends of the length comprising a head end and a foot end of the patient support. The patient support is mounted on a wheeled base including four-floor surface engaging and castered wheels spaced from one another. The wheeled base has an imaginary transverse centerline located at a midpoint of the length thereof. An auxiliary wheel support structure secured to the wheeled base suspendedly supports auxiliary wheels. The wheeled carriage includes a control apparatus for controlling the auxiliary wheel support structure to move the auxiliary wheels to a first deployed position engaging the floor surface, while a pair of castered wheels at the foot end are lifted from the floor surface. The control apparatus can also move the auxiliary wheels to a second stored position out of engagement with the floor surface.
When the auxiliary wheels are positioned on an uneven floor surface, such that the deployed auxiliary wheels are out of engagement with the floor surface while the castered wheels contact the floor, the auxiliary wheel support structure enables the auxiliary wheels to move downwardly to maintain contact with the floor surface.
In a first embodiment, the auxiliary wheel support structure includes a floating frame supporting the auxiliary wheels. When the deployed auxiliary wheels begin to lose contact with the floor surface due to a lowered surface thereunder, the floating frame moves downwardly to maintain contact between the auxiliary wheel and the lowered floor surface.
In a second embodiment, the auxiliary wheel support structure includes a pair of spaced parallel frame members secured to a cross bar that supports a cam follower and a roller member. A cam apparatus controls the cam follower to place the auxiliary wheels in a deployed or stored position. The auxiliary wheel support structure includes a linkage element pivotally secured to the wheeled base, and receiving the roller member at a first end. A push rod is pivotally secured at a first end to the wheeled base and pivotally and slidably secured at a second end to the linkage element. A rod spring mounted about and along the length of the rod member applies a biasing force therethrough, which is transferred through the roller member to the cam follower. When in the deployed position, the rod spring maintains a downward force on the cam follower. Then, when the four castered wheels contact the floor surface and the auxiliary wheel would not, because of an uneven surface, the downward force lowers the cam follower and thus the auxiliary wheels, to maintain floor surface contact.
Another embodiment provides a drive motor for driving the deployed auxiliary wheels to power the wheeled carriage. A handle on the wheeled carriage controls the velocity and direction of the wheeled carriage. The handle applies force to a load cell in one of two opposing directions. Applying force to the handle in a first forward direction accelerates the carriage in the forward direction, or decelerates the carriage when traveling in the reverse direction. When traveling in the reverse direction, as long as the forward force remains, the carriage eventually stops and then restarts beginning movement in the forward direction.
Another embodiment provides a disconnect mechanism for disconnecting the drive motor from a powered driving mode to a manually controlled unpowered operating mode. The unpowered mode allows an operator to manually move the wheeled carriage.
Another embodiment includes a drive and control system for controlling the auxiliary wheel support structure to move said at least one auxiliary wheel between a first deployed position and a second stored position out of engagement with the floor surface. The drive and control system receives a drive signal from an input measuring device, compares the value with a drive signal threshold value, and provides a power signal to drive the auxiliary wheel in response to the value of and the direction of the drive signal when the drive signal value exceeds the drive signal threshold value. The drive signal threshold value changes at increasing velocities of the vehicle. The drive and control system includes a processor which stores and calculates the threshold value. The drive and control system operates to smoothly and methodically control the velocity of the wheeled carriage.